The dating site e Harmony claims an average of 542 members marry every day in America.

As online dating becomes the dominant path to relationships, it shifts the way these unions are built.

The question, casting forward, is how that will change the very institution that many daters seek—marriage.

And they share some common conceits: that similarity is good for a relationship, and that mathematical algorithms can predict compatibility.At a press launch, Facebook reps showed off the new product, explaining that it could be used to search for restaurants, or for job recruiting.At one point, a Facebook employee stood to demonstrate a search for “friends of my friends who are single and living in San Francisco.” And that’s when Facebook entered the online dating game, doing away with what was, until now, a fragile divide between quotidian online activity and the act of browsing for potential mates.In 2003, a young Mark Zuckerberg sat in front of his computer and instant-messaged a friend.Back then, “the facebook thing” was still a rough idea, and 18-year-old Zuckerberg was trying to finesse the concept. “I don’t think people would sign up for the facebook thing if they knew it was for dating,” Zuckerberg wrote.